Enhancing the Performance of Perovskite Solar Cells with CPMIMBF₄ Ionic Liquid Additives

Perovskite solar cells (PSCs) have attracted widespread attention due to their excellent photovoltaic performance. The two-step solution method for perovskite films offers ease of operation and reproducibility compared to the one-step solution method. However, the crystallization process of perovskite is difficult to control, resulting in low-quality perovskite films. Herein, we introduce an ionic liquid additive of 1-cyanopropyle-3-methylimidazolium tetrafluoroborate (CPMIMBF 4 ) into a PbI 2 precursor to improve the device performance. The CPMIMBF 4 additive serves as a bridge between PbI 2 and dimethyl sulfoxide (DMSO), effectively inhibiting the rapid nucleation rate of PbI 2 and promoting the formation of a PbI 2 film with high crystallinity, which increases the ability of PbI 2 to react with organic ammonium salt solutions. By using the CPMIMBF 4 additive, we obtained the optimal (001)-oriented perovskite film, enhanced the quality of the perovskite film, and reduced the trap density of the devices. And the imidazole cations (CPMIM + ) remain on the surface of the perovskite, forming a hydrophobic protective layer and passivating uncoordinated Pb 2+ . At the same time, the BF 4 – anions fill the vacancy left by I – . Ultimately, we achieved a power conversion efficiency (PCE) of 24.25% for PSCs on TiO 2 substrates. This study provides a perspective for the application of multifunctional ionic liquids in PSCs.